add a slash command to grant sandbox read access to inaccessible directories (#11512)

There is an edge case where a directory is not readable by the sandbox.
In practice, we've seen very little of it, but it can happen so this
slash command unlocks users when it does.

Future idea is to make this a tool that the agent knows about so it can
be more integrated.

codex-rs/tui/src/app_event.rs

@@ -218,6 +218,19 @@ pub(crate) enum AppEvent {
         preset: ApprovalPreset,
     },
 
+    /// Begin a non-elevated grant of read access for an additional directory.
+    #[cfg_attr(not(target_os = "windows"), allow(dead_code))]
+    BeginWindowsSandboxGrantReadRoot {
+        path: String,
+    },
+
+    /// Result of attempting to grant read access for an additional directory.
+    #[cfg_attr(not(target_os = "windows"), allow(dead_code))]
+    WindowsSandboxGrantReadRootCompleted {
+        path: PathBuf,
+        error: Option<String>,
+    },
+
     /// Enable the Windows sandbox feature and switch to Agent mode.
     #[cfg_attr(not(target_os = "windows"), allow(dead_code))]
     EnableWindowsSandboxForAgentMode {